In a storage system, there may be different types of I/Os for a given storage device. For example, important configuration information (such as status information of various components or the like) of the storage system and user data may be stored on the same storage device. An I/O for the important configuration information and an I/O for the user data typically have different priorities. The configuration information of the storage system is of critical importance for the storage system, and data loss in the configuration information may probably result in serious problems. Therefore, an I/O for the important configuration information usually has a higher priority than an I/O for the user data. In other words, the performance of the I/O for the configuration information must be guaranteed, i.e., the I/O must be completed within the required time and the throughput thereof must be guaranteed.